1. Field of the Invention
This invention relates to a technique for detecting a displacement of a movable positioning object with respect to a reference position.
2. Description of the Related Art
As a technique for detecting the position of a movable positioning object or determining whether or not the positioning object is positioned at a designated position, the positioning object is imaged using an imager such as a camera and the position of the positioning object in an image is detected by an image analysis. For example, in a technique described in JP 2015-152475A, a processing nozzle configured to be movable with respect to a substrate and discharge a liquid or the like is a positioning object. A displacement amount in an actual space is approximately obtained by multiplying a displacement amount of the processing nozzle in an image imaged by the camera by a proportionality coefficient corresponding to an imaging magnification.
In the above conventional technique, whether or not the positioning of the nozzle as the positioning object is good is determined based on whether or not the displacement amount of the positioning object with respect to a proper position designated in advance as a reference is within an allowable range. The displacement amount to be evaluated this time is the one in the actual space, but not the one in the imaged image. A relationship between the displacement amount in the actual space and that in the image is not necessarily linear due to a moving mode of the positioning object and a positional relationship with the imager. Thus, detection accuracy may be insufficient in some cases with the method for obtaining the displacement amount in the actual space by multiplying the displacement amount in the image by the proportionality coefficient.